1. Technical Field
The present disclosure relates to the field of integrated circuit dies. The present disclosure relates more particularly to temperature sensors in integrated circuit dies.
2. Description of the Related Art
The physical properties of the semiconductor substrate affect the functionality of the integrated circuit. The physical properties of the semiconductor substrate are in turn affected by the temperature of the semiconductor substrate.
Integrated circuits generally comprise numerous transistors formed near the surface of a semiconductor substrate. To form transistors the semiconductor substrate is doped at selected areas with donor and acceptor impurity atoms to alter the conductivity of the semiconductor and to provide the desired carrier type. The electron (a negative charge) is the majority carrier in a semiconductor doped with donor atoms. The hole (a positive charge) is the majority carrier in a semiconductor doped with acceptor atoms. The current and voltage characteristics of a transistor depend in part on the effective mobility of the charge carriers.
The physical properties of doped and undoped semiconductor materials are temperature dependent. The mobility of charge carriers in a semiconductor lattice varies with temperature. The conductivity of undoped silicon also depends on temperature. The conductive characteristics of the transistor are heavily dependent on temperature. The switching speed and performance of the transistors are in turn affected by the conductive characteristics of the transistor. The output characteristics of an integrated circuit containing millions or even billions of transistors can be greatly affected by temperature.
Integrated circuits generally comprise many other kinds of circuit elements whose characteristics are also dependent on temperature. Integrated circuits are formed of many interconnecting metal lines formed within a multilevel dielectric stack. The physical characteristics of the metal lines and the layers of the dielectric stack also depend on temperature. The temperature dependence of all of these components of an integrated circuit makes the output characteristics of the integrated circuit dependent on temperature.
Many factors affect the temperature of an integrated circuit. The very use of an integrated circuit will change its temperature. As an integrated circuit is used, the large amounts of current flowing through the many circuit elements cause the temperature of the integrated circuit to increase. The heat generated by the integrated circuit increases and decreases as the demand on the integrated circuit increases and decreases. Thus an integrated circuit can undergo large changes in temperature based solely on its own performance requirements from moment to moment.
In some integrated circuit dies, it is beneficial to know the temperature of particular regions of the integrated circuit die. For this reason some integrated circuit dies include multiple temperature sensors to monitor the temperature of the die at a particular location. Each temperature sensor includes a respective analog-to-digital converter to convert the analog signal output by the temperature sensor to a digital signal. As the complexity of integrated circuit dies has increased, so has the demand for more precise temperature calculations. In order to provide more precise temperature calculations, each analog-to-digital converter must output a digital temperature signal having more bits. In order to output a digital signal with more bits, a larger analog-to-digital converter is needed. With multiple temperature sensors on the integrated circuit die, a very large area of semiconductor substrate is required to accommodate the multiple large analog-to-digital converters.